Trans-4-alkyloxymethyl-1-(4&#39;-substituted biphenylyl-4)cyclohexanes

ABSTRACT

Novel liquid crystal compounds having a higher clearing point and a superior stability are provided, which are trans-4-alkyloxymethyl-1-(4&#39;-substituted biphenylyl-4)cyclohexanes expressed by the general formula (I): ##STR1## wherein R 1  and R 2  each represent an alkyl group of 1 to 8 carbon atoms and n represents 0 or 1.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel liquid crystal compounds and liquidcrystal compositions containing the same.

2. Description of the Prior Art

Liquid crystal display elements utilize the optical anisotropy anddielectric anisotropy of liquid crystal substances and are classifiedinto TN type (twisted nematic type), DS type (dynamic scattering type),guesthost type, DAP type, etc. according to their modes based onprinciple. Due to differences between these modes, the optimumcharacteristics of liquid crystal substances suitable to theirrespective uses are different. At any rate, however, it is common tothese liquid crystal substances that they are required to be stable tomoisture, air, heat, light etc. Further, they are required to be capableof existing in the form of a liquid crystal phase at least in the rangeof 0° to 60° C. However, no single compound exists which satisfies allof these conditions, but it is the present status that mixtures ofseveral kinds of liquid crystal compounds or non-liquid crystalcompounds have been practically used as a liquid crystal composition.

SUMMARY OF THE INVENTION

The object of the present invention is to provide compounds which areuseful as a component constituting liquid crystal compounds useful forTN display elements, and particularly effective for raising their N-Ipoint (clearing point).

The compounds of the present invention aretrans-4-alkyloxymethyl-1-(4'-substituted biphenylyl-4) cyclohexanesexpressed by the following general formula (I): ##STR2## wherein R₁ andR₂ each represent an alkyl group of 1 to 8 carbon atoms preferably 1 to5 carbon atoms and n represents 0 or 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The compounds of the present invention are novel liquid crystalcompounds having a higher clearing point and a superior stability. Thesecompounds cannot be singly applied for practical use, but due to theirsuperior compatibility with other liquid crystal compounds, when theyare admixed with one kind of a mixture of several kinds of liquidcrystals of e.g. biphenyl group, ester group, azoxy group,cyclohexanecarboxylic acid ester group, phenylcyclohexane group,phenylpyrimidine group, phenylmetadioxane group, etc., they are efectivefor raising their clearing point. Moreover, when the compounds of thepresent invention are used, it is possible to extend the temperaturerange on the lower temperature side and thereby provide a liquid crystalcomposition having superior low temperature response characteristics.

Compounds of the formula (I) are prepared through the following steps:##STR3##

First, trans-4-phenylcyclohexanecarboxylic acid methyl ester (II) (W. S.Johnson et al, J.A.C.S., 67, 1045 (1945)) which is a known substance isreduced with a reducing agent such as lithium aluminum hydride (LiAlH₄)or according to a known reduction method to obtaintrans-4-phenylcyclohexylmathanol (III), which is then reacted withp-toluenesulfonyl chloride in dry pyridine to obtain p-toluenesulfonicacid trans-4-phenylcyclohexyl methyl ester (IV), which is then reactedwith an alcoholate to obtain atrans-4-alkyloxymethyl-1-phenylcyclohexane (V), which is then heatedtogether with iodine and hydroiodic acid in a solvent such asN,N-dimethylformamide, dimethylsulfoxide, etc. to obtain atrans-4-alkyloxymethyl-1-(4'-iodophenyl)cyclohexane (VI), the iodine ofwhich is then replaced by Li with a hexane solution of n-butyllithium(n-C₄ H₉ Li) to obtain a ##STR4## which is further reacted with a4-substituted cyclohexanone to obtain atrans-4-alkyloxymethyl-1-(4'-substituted cyclohexenyl phenyl)cyclohexane(VII) which is then heated together with a dehydrogenating agent in aninert organic solvent such as toluene, xylene, etc. to obtain a compoundof the formula (I) of the present invention.

When, in the above third step, the compound (IV) is reacted with as analcoholate, sodium methoxide, sodium ethoxide, sodium propoxide, sodiumbutoxide, sodium pentoxide, sodium hexyloxide, sodium heptyl oxide,sodium octyloxide, respectively, and in the fifth step, there is used4-methylcyclohexanone, 4-ethylcyclohexanone, 4-propylcyclohexanone,4-butylcyclohexanone, 4-pentylcyclohexanone, 4-hexylcyclohexanone,4-heptylcyclohexanone, 4-octylcyclohexanone,4-(trans-4-methylcyclohexyl)cyclohexanone,4-(trans-4-ethylcyclohexyl)cyclohexanone,4-(trans-4-propylcyclohexyl)cyclohexanone,4-(trans-4-butylcyclohexyl)cyclohexanone,4-(trans-4-pentylcyclohexyl)cyclohexanone,4-(trans-4-heptylcyclohexyl)cyclohexanone, or4-(trans-4-octylcyclohexyl)cyclohexanone, then it is possible to prepareas final products, compounds of the formula (I) wherein R₁ and R₂ areeach various kinds of alkyl groups.

Next, preparation, properties and use of the compounds of the presentinvention will be described in detail by way of Examples.

EXAMPLE 1

Preparation oftrans-4-methyloxymethyl-1-(4'-propylbiphenylyl-4)cyclohexane (a compoundof the formula (I) wherein n=O, R₁ =CH₃ and R₂ =C₃ H₇)

First step

Dry tetrahydrofuran (THF)(420 ml) was added to lithium aluminum hydride(11.1 g, 0.293 mol), and while the mixture was vigorously agitated,there was dropwise added a soltuion obtained by dissolvingtrans-4-phenylcyclohexanecarboxylic acid methyl ester (II) (64.0 g,0.293 mol) in THF (70 ml), at a reaction temperature kept at 20° C. orlower. After completion of the addition, the reaction mixture was warmedup to 55° C., followed by reacting it for 2 hours and cooling. Ethylacetate (12 ml) and water (100 ml) were then added, followed by adding a1N aqueous solution of sulfuric acid (350 ml) to dissolve inorganicmatter, separating the resulting organic layer and aqueous layer fromone another, adding n-heptane (200 ml) to extract the organic layer,washing the extract solution with water 500 ml), then washing with a 2%aqueous solution of Na₂ CO₃, further washing with water until theaqueous layer became neutral, distilling off n-heptane and THF,recrystallizing the resulting solid as residue from n-heptane (20 ml),filtering off crystals and drying to obtain 4-phenylcyclohexylmethanol(III) (51.4 g). M.P. 47.3°˜48.5° C.

Second step

Compound (III) (50 g, 0.268 mol) was dissolved in dry pyridine (110 ml)and cooled to 5° C. or lower. To this solution was dropwise added asolution of p-toluenesulfonic chloride (50.1 g, 0.263 mol) dissolved indry toluene (70 ml), through a dropping funnel in small portions so thatthe reaction temperature could not exceed 10° C. After completion of theaddition, the cooling bath was removed and agitation was carried out atroom temperature for 4 hours, followed by adding water (100 ml) andtoluene (300 ml) to extract the resulting product, washing thetoluene-extraction liquid twice with 6N-HCl (100 ml), then once withwater (200 ml), further twice with 2N aqueous solution of NaOH (100 ml),and 4 times with water (200 ml), distilling off the solvent,recrystallizing the residue from toluene (90 ml), filtering off anddrying to obtain p-toluenesulfonic acid trans-4-phenylcyclohexyl methylester (IV) (77.0 g). M.P. 108.0°˜108.7° C.

Third step

Slices of metal Na (17.4 g, 0.755 mol) were added in small portions tomethyl alcohol (250 ml) agitated at room temperature to prepare sodiummethoxide. After metal Na pieces disappeared, a solution obtained bydissolving the compound (IV) (200.0 g, 0.581 mol) obtained above, in drytoluene (600 ml), was gradually added through a dropping funnel so thatthe inner temperature could keep within a range of 50° to 60° C. Aftercompletion of the addition, the mixture was refluxed for 4 hours,followed by cooling, adding water (20 ml), transferring into aseparating funnel, washing the resulting toluene layer with water untilthe aqueous layer became neutral, distilling off toluene under reducedpressure, distilling under reduced pressure and collecting fractions ofboiling points of 105°˜108° C./1.5 mmHg to obtaintrans-4-methyloxymethyl-1-phenylcyclohexane (V) (100.0 g).

Fourth step

Into a 1 l three-neck flask were added the compound (V) (100.0 g, 0.489mol) obtained at the third step, acetic acid (344 ml), water (91 ml),hydroiodic acid (20.6 g, 0.117 mol), iodine (54.5 g, 0.215 mol), CCl₄(40 ml), and conc. hydrochloric acid (14 ml), followed by stirring,heating under reflux for 3 hours for reaction, cooling, adding a 10%aqueous solution of sodium thiosulfate (15 ml), reducing excess iodine,adding n-heptane (200 ml) to extract the resulting product, washingn-heptane layer with water until the aqueous layer became neutral,distilling off n-heptane under reduced pressure, dissolving the residuein n-hexane (50 ml), allowing the solution to stand at -10° to -20° C.for 12 hours, filtering off the resulting crystals and drying to obtain4-(trans-4'-methyloxy-methylcyclohexyl)iodobenzene (VI) (81.3 g). M.P.40.3°˜42.3° C.

Fifth step

Into a 500 ml three-neck flask were placed the compound (VI) (21 g,0.064 mol) obtained at the fourth step and dry toluene (40 ml) in drynitrogen atmosphere, followed by dissolving with stirring. To thesolution was dropwise added a commercially available 1.67N hexanesolution (42.7 ml) of n-butyllithium (0.067 mol) over about 10 minutesat a liquid temperature kept at 20° to 25° C. After completion of theaddition, the mixture was kept at 25° C. for 30 minutes, and then cooledto 5° C., followed by dropwise adding 4-propylcyclohexanone (11.2 g,0.08 mol) over 20 minutes while the temperature was kept at 5° to 10°C., further keeping the temperature at 45° C. for 30 minutes, dropwiseadding water (20 ml), further dropwise adding 6N-HCl (40 ml) while thetemperature was kept at 30° C. or lower, separating off the resultingorganic layer, adding potassium hydrogen sulfate (KHSO₄) (2 g),distilling off the solvent on heating, concentrating until the liquidtemperature reached 110° C., during which dehydration reactionproceeded, cooling, transferring into a separating funnel, washing theresulting organic layer with water, distilling off the solvent,recrystallizing the residue from ethyl alcohol (10 c.c.) to obtaintrans-4-methyloxymethyl-1-(4'-methyl-1-cyclohexenylphenyl)cyclohexane(VII)(5.3 g) having a melting point (C-S point) of 64° C., a S-N pointof 93.4° C. and a clearing point (N-I point) of 14.3° C.

Sixth step

In a 300 ml three-neck flask were mixed together the compound (VII) (5.3g, 0.016 mol) obtained at the fifth step, chloranil (9.2 g, 0.037 mol)and xylene (76 ml), followed by heating under reflux for 24 hours,cooling, filtering off insoluble solids, concentrating to remove xylene,and recrystallizing the resulting raw crystals from ethyl alcohol toobtain the objective purified compound,trans-4-methyloxymethyl-1-(4'-propylbiphenylyl-4)cyclohexane (0.5 g),which had a melting point (C-N point) of 122.4° C. and a clearing point(N-I point) of 157.1° C. The elemental analysis values accorded wellwith calculated values as follows:

    ______________________________________                                                           Calculated values (%)                                      Observed values (%)                                                                              (in terms of C.sub.23 H.sub.30 O)                          ______________________________________                                        C       85.62          85.66                                                  H       9.30           9.38                                                   ______________________________________                                    

EXAMPLES 2˜4

Example 1 was repeated except that methyl alcohol was replaced by ethylalcohol (Example 2) or propyl alcohol (Examples 3 and 4) at the thirdstep of Example 1, and also 4-propylcyclohexanone was replaced by4-methylcyclohexanone (Example 2), 4-ethylcyclohexanone (Example 3) or4-butylcyclohexanone (Example 4) at the fifth step of Example 1, toobtain compounds of Examples 2˜4 listed in Table 1. The values of theirphysical properties are shown in Table 1 together with the results ofExample 1.

                  TABLE 1                                                         ______________________________________                                                     Phase transition point (%)                                       Exam-  In Formula (I)                                                                            C-N              S-N   N-I                                 ple    R.sub.1 R.sub.2 point C-S point                                                                              point point                             ______________________________________                                        1      CH.sub.3                                                                              C.sub.3 H.sub.7                                                                       122.4 --       --    157.1                             2      C.sub.2 H.sub.5                                                                       CH.sub.3                                                                               90.7 --       --    139.5                             3      C.sub.3 H.sub.7                                                                       C.sub.2 H.sub.5                                                                       --    room temp.                                                                             115.6 124.2                                                          or lower                                         4      C.sub.3 H.sub.7                                                                       C.sub.4 H.sub.9                                                                       --    room tem-                                                                              --    125.1                                                          perature       (S-I)                                                          or lower                                         ______________________________________                                    

EXAMPLE 5

Preparation oftrans-4-methyloxymethyl-1-[4'-(trans-4-propylcyclohexyl)biphenylyl-4]-cyclohexane(a compound of the formula (I) wherein n=1, R₁ =CH₃ and R₂ =C₃ H₇)

First step to fifth step

Into a 500 ml three-neck flask were placed compound (VI) (27.7 g, 0.084mol) prepared in the same manner as the first step to the fourth step inExample 1, and dry toluene (60 ml), followed by dissolving at 20° C.with stirring. To the solution was dropwise added a commerciallyavailable 1.67N hexane solution (6.3 ml) of n-butyllithium (0.100 mol)over about 10 minutes while the liquid temperature was kept at 20° to25° C., followed by keeping the temperature at 25° C. for 30 minutes,cooling to 5° C., dropwise adding a solution obtained by dissolving4-(trans-4-propylcyclohexyl)cyclohexanone (19.5 g, 0.088 mol) in drytoluene (30 ml), through a dropping funnel so that the inner temperaturecould not exceed 10° C., keeping the temperature at 45° C. for 30minutes, cooling, adding water (30 ml) and 6N-hydrochloric acid (60 ml),separating the resulting layers, adding potassium hydrogen sulfate(KHSO₄) (3 g) to the organic layer, distilling off the solvent byheating, concentrating until the liquid temperature reached 110° C.,during which dehydration reaction proceeded, cooling, transferring intoa separating funnel, washing the organic layer three times with water,distilling off the solvent, and recrystallizing the residue from ethylacetate (20 ml) in a refrigerator to obtain a compound (VII) (15 g),which had a C-S point of 208.0° C., a S-N point of 234.1° C. and a N-Ipoint of 280° C. or higher.

Sixth step

In a 200 ml three-neck flask were placed the above compound (VII) (4.8g, 0.012 mol), chloranil (6.7 g, 0.027 mol) and xylene (60 ml), followedby refluxing for 24 hours, cooling, filtering off the resultinginsoluble crystals, distilling off xylene, recrystallizing the resultingraw crystals from ethyl acetate (10 ml), filtering off and drying toobtain the objectivetrans-4-methyloxymethyl-1-[4'-(trans-4-propylcyclohexyl)biphenylyl-4]cyclohexane(1.3 g), which had a C-S point of 143.5° C., a S -N point of 196.1° C.and a N-I point of 280° C. or higher. The elemental analysis values ofthis product accorded well with the calculated values as follows:

    ______________________________________                                                          Calculated value (%)                                        Observed value (%)                                                                              (in terms of C.sub.29 H.sub.40 O.sub.1)                     ______________________________________                                        C       86.03         86.08                                                   H       9.94          9.97                                                    ______________________________________                                    

EXAMPLES 6 AND 7

Example 1 was repeated except that methyl alcohol was replaced by ethylalcohol or propyl alcohol at the third step of Example 1 to obtain thecorresponding sodium alkoxide which were then reacted withp-toluenesulfonic acid and trans-4-phenylcyclohexyl methyl ester as inExample 1, followed by collecting fractions of 112°˜115° C./1.5 mmHg and127°˜130° C./1.5 mmHg to obtaintrans-4-ethyloxymethyl-1-phenylcyclohexane ortrans-4-propyloxymethyl-1-phenylcyclohexane, wherebytrans-4-ethyloxymethyl-1-[4'-(trans-4-propylcyclohexyl)biphenylyl-4]cyclohexane(C-S point, 98.1° C.; S -N point, 202.6° C.; N-I point, 280° C. orhigher) ortrans-4-propyloxymethyl-1-[4'-(trans-4-propylcyclohexyl)biphenylyl-4]cyclohexane(C-S point, 74° C.; S -N point, 228° C.; N-I point, 280° C. or higher)was prepared.

EXAMPLE 8 (USE EXAMPLE 1)

A liquid crystal composition consisting of

    ______________________________________                                         ##STR5##           25.5 parts by weight                                       ##STR6##           34.0 parts by weight, and                                  ##STR7##           25.5 parts by weight,                                     ______________________________________                                    

had a nematic liquid crystal temperature range (MR) of -3° to 52.5° C.,a viscosity at 20° C., η₂₀ of 23 cp, a dielectric constant anisotropy Δεof 11.3 (ε.sub.∥ =16.2 and ε.sub.⊥ =4.9) and a refractive indexanisotropy Δn=0.120, and when it was sealed in TN cell of 10 μmthickness, the resulting threshold voltage and saturation voltage were1.50 V and 2.20 V, respectively.

To this composition was added a compound of Example 2, ##STR8## as oneof the compounds of the present invention (15 parts by weight) to obtaina liquid crystal composition which had a MR of -3° to 60.7° C., that is,its N-I point was raised, and also had a η₂₀ of 24.8 cp, a Δε of 10.2ε.sub.∥ =14.7 and Δ.sub.⊥ =4.5) and a Δn of 0.128, and when it wassealed in the same cell as above, the threshold voltage and saturationvoltage were 1.66 V and 2.26 V, respectively.

EXAMPLE 9 (USE EXAMPLE 2)

A liquid crystal composition consisting of

    ______________________________________                                         ##STR9##           28.57 parts by weight                                      ##STR10##          38.09 parts by weight, and                                 ##STR11##          28.57 parts by weight,                                    ______________________________________                                         had a nematic liquid crystal temperature range (MR) of -3° to     52.5° C., a viscosity at 20° C., η.sub.20 of 23 cp, and     a dielectric constant anisotropy Δε of 11.3     (ε.sub.∥ =16.2 and ε.sub.⊥ =4.9), and when     it was sealed in a TN cell of 10 μm thickness, the resulting threshold     voltage and saturation voltage were 1.5 V and 2.2 V, respectively.

To this composition was added a compound ##STR12## as one of thecompounds of the present invention (4.76 parts by weight) to obtain aliquid crystal composition which had a MR broadened to -3° to 61.0° C.,a η₂₀ of 25 cp, and a Δε of 10.8 (ε.sub.∥ =15.3 and ε.sub.⊥ =4.5) andwhen it was sealed in the same cell as above, the threshold voltage andsaturation voltage were 1.62 V and 2.30 V, respectively.

We claim:
 1. A compound, expressed by the formula ##STR13## wherein R₁and R₂ each represents an alkyl group of 1 to 8 carbon atoms.
 2. Aliquid crystal composition comprising a mixture of compounds at leastone of which is a compound expressed by the formula of claim
 1. 3. Acompound of claim 1, expressed by the formula ##STR14## wherein R₁ andR₂ each represents an alkyl group of 1 to 5 carbon atoms.